Nicole never got along with her young sister Alice.

[alpacinou]

Is this correct and natural?

Nicole never got along with her younger sister. Nicole saw too much of herself in Alice and she hated that. She wanted to be unique, one of a kind. Perhaps if they were identical twins, she would have killed Alice.

 

[5jj]

Perhaps if they had been identical twins, she would have killed Alice.

 

[emsr2d2]

You don't need both "unique" and "one of a kind". It's tautologous.